The use of polyester compositions as a packaging material, particularly, compositions comprising polyethylene terephthalate, generally referred to as "PET", in the form of films, plastic bottles and other containers is well known. Plastic bottles are used for containing pressurized fluids such as carbonated drinks, e.g., soft drinks or mineral waters, as well as for non-carbonated, non-pressurized drinks. To form plastic bottles, the polymer is extruded and then formed into chips. The chips are employed to make a bottle preform by injection molding as is well known in the industry. The preform is then reheated and blown into a mold which provides the final shape of the bottle.
During the manufacture of bottles, one problem often encountered is that of "stickiness", wherein the newly formed bottles or bottle preforms have a tendency to stick to surfaces, including each other. This can give rise to problems during the conveying and palletizing of the bottles which disrupt operations. While various approaches to solving this bottle problem have been tried, none have been satisfactory until the invention disclosed herein, particularly under economic considerations which require high production rates.
The approach to solving the stickiness problem disclosed herein is to increase the surface roughness of the bottles by the addition of particulate matter to the resin prior to using the resin to form bottles. With increased roughness, bottle-to-bottle or bottle-to-other-surface contact will be minimized, or the bottles will have a lesser tendency to stick to each other and will thus not cause interruptions in operations. While a variety of substances have been evaluated for reducing stickiness, including fumed silica (sometimes called pyrogenic silica), colloidal silica and silica beads, it has been determined that amorphous and fumed silicas are most advantageous for reducing stickiness.
Silica has been used in the production of polyester films for a variety of uses. For example, U.S. Pat. Nos. 5,384,191 and 5,266,397 to Ogawa et al. describe the preparation of an amorphous silica filler and its incorporation into a film resin to improve, among other things, the scratch resistance properties of the surface of films prepared using such resin; U.S. Pat. No. 5,281,379 to Noguchi et al. describes a process for producing thermoplastic resin compositions which includes adding fine particles, including silica, of less than 10 .mu.m particle size to a variety of polymer resins, including polyester resins. Other U.S. Patents teaching polyester resins suitable for the production of films and including, among other things, silica in combination with a polyester resin, are U.S. Pat. No. 5,475,046 to Son et al. (polyester with macro particles of silica and aluminum oxide); U.S. Pat. No. 5,382,651 to Kim et al (polyester with silica produced from an ethylene glycol silica sol); U.S. Pat. No. 5,336,709 (undrawn polyester yarns containing fumed silica); U.S. Pat. Nos. 5,278,221 and 5,278,205 (polyester film containing glass beads and fumed silica); and U.S. Pat. No. 4,029,289 (polyester film resin containing pyrogenic aluminum and pyrogenic silica). While film resins have incorporated various silicas for a variety of reasons, similar teachings have not been found in the art related to polyester resins suitable for use in the production of containers, particularly bottles. This is most likely due to the fact that incorporation of particulates into bottle resins causes haziness, making the resins unsuitable for many bottle uses.
Therefore, it is a object of the invention to describe polyester resins incorporating, among other things, fumed silica, colloidal silica, precipitated silica and silica beads, and a process for producing such resins. Fumed silicas are preferred.
A further object of this invention is to describe polyester resins suitable for the production of containers which incorporate, among other things, fumed silica to improve the processing characteristics of such resins and the products made therefrom, and a process for producing such resins.
An additional object of this invention is to describe polyester resins comprising, among other things, polyethylene terephthalate, and similar terephthalate polyesters, and fumed silica, and a process for making same.
A further object of the invention is to describe a resin comprising, among other things, polyethylene terephthalate and fumed silica which is suitable for the production of beverage containers and which has improved handling characteristics during the production of same.